Your fallacy is assuming that the desire for kids is passed on to children. If that were so, people without the desire to have kids would have died out thousands of years ago. Reality disagrees with that conclusion.

I think GP's point is more along the lines that people who care less about grand things like society and the planet tend to also reproduce more.

... and consume less, because their baseline for consumption is typically shared multi-generational living and relative poverty in a developing country.

Not necessarily. This works for developed countries too. As an illustration, see e.g. the premise of the movie "Idiocracy".

The theory of evolution implies that the desire for kids must be passed on to children. The modern environment just means that genes that formerly led to positive results in the environment we evolved in, in the modern environment accidentally make people vulnerable to antinatalism. If the modern environment persists, those genes will die out.